An article at Onion made me consider what might be a better way to control floods and it seems that the creation of holes near streams that could function as overflow valves, upstream of the point where they combine is far better than attempting to control it after it has combined in force. If a farmer simply kept a hole on their farm that fills up from the stream when it is high enough, then the combined action of individuals would do what the government cannot. The water doesn't just magically appear at the point of the flood, it has to be sourced from thousands of little streams. ( or more precisely drops )

That wouldn't help New Orleans, but maybe I will think of something for that before the next hurricane.